According to a recent study published on bmj.com, annual screening may not help prevent women from dying from breast cancer.

Canadian researchers found in a 25-year study that annual breast cancer screenings of women between ages 40 and 59-years-old did not reduce mortality rate from the condition.

The team compared breast cancer incidence and mortality up to 25 years in over 89,000 women who did or did not undergo mammography screening. These tests are done regularly to help prevent mortality rates with breast cancer, and other studies have shown that women with small breast cancer detected by screening have a better long term survival than women with palpable breast cancer. However, researchers have not been clear as to whether this survival difference is a consequence of organized screening or of lead time bias.

Women who participated in mammography screening were tested every year over a five year period. The women who did not participate in the exams were used as a control group for the study. Women in their 40s also received annual physical breast examinations.

During the study, 3,250 women who underwent mammography screening and 3,133 who did not were diagnosed with breast cancer. Of those women, 500 in the mammography screen died, while 505 in the control group passed away.

“Thus, the cumulative mortality from breast cancer was similar between women in the mammography arm and in the control arm,” the authors wrote in the online journal.

The team found that 22 percent of the mammography screens that detected invasive cancers were over-diagnosed, meaning there is about one over-diagnosed breast cancer for every 424 women who received mammography screening.

The researchers said the results may not be generalizable to all countries, but for technically advanced countries the results support the idea that policy makers should reassess the rationale for mammography screenings. They also stressed that education, early diagnosis and excellent clinical care are important, but annual mammography does not result in a reduced chance of dying from breast cancer.

Dr Mette Kalager and colleagues, who were not a part of the study, wrote in an accompanying article that long term follow-up does not support screening women under 60.

“The rationale for screening by mammography be urgently reassessed by policy makers,” Kalager and colleagues wrote. They added that this is not an easy task “because governments, research funders, scientists, and medical practitioners may have vested interests in continuing activities that are well established.”